A check valve structure that is advantageously used for a liquid pump, an oxygen concentrator, a hemodialysis circuit, an infusion circuit and the like, limits the flow of a fluid such as a liquid only in a forward flow direction, and prevents the flow in the reverse flow direction is well known. A so-called umbrella-type valve element, which includes, for example, an umbrella-shaped portion having a substantially circular shape in a plan view and a shaft portion provided substantially at the center of the umbrella-shaped portion, and which is configured of an elastically deformable elastic material (for example, a rubber material such as silicone rubber) is known as a valve element constituting the check valve structure (see PTL 1).